PROJECT SUMMARY Artemisinin-based combination therapies are the most effective frontline treatments for Plasmodium falciparum malaria; therefore, the recent emergence and potential spread of artemisinin resistance in Southeast Asia, the epicenter of multidrug-resistant P. falciparum, has raised global concerns. Studies of clinical isolates from western Cambodia and genetically modified laboratory strains have established a causal link of artemisinin resistance with mutations in the K13 gene (Pf3D7_1343700), but the molecular mechanism of K13-mediated artemisinin resistance is not understood. Population genetic studies of parasites from Southeast Asia showed independent emergence of the K13 mutants in multiple parasite populations. To further address this urgent problem, this U.S.-China joint project will (1) identify novel molecular markers associated with artemisinin resistance through a genome-wide association study of P. falciparum parasite isolates from the China- Myanmar border area, where artemisinin family drugs have the longest history of deployment; (2) perform functional studies to determine the role of the K13 gene and its polymorphisms in artemisinin resistance; and (3) elucidate the molecular mechanism of artemisinin resistance through the identification of the molecular complex of the K13 protein. This joint project, built on a solid foundation of our past collaboration, encompasses the complementary expertise and resources from the collaborating institutions. The proposed studies will take advantage of the large archive of culture-adapted P. falciparum clinical isolates collected from the China-Myanmar border area and the significant inroad we have made into this field from our earlier collaborations. Information generated from this study will be highly useful for monitoring, curbing and deterring the spread of artemisinin resistance, and will have far-reaching impacts on both regional and global malaria elimination campaigns.